Fibrous electrode material

ABSTRACT

A biomimetic electrode material including a fibrous matrix including a conductive polymer and an ion conducting polymeric material is described. The biomimetic electrode material may be used in a number of body-implantable applications including cardiac and neuro-stimulation applications. The biomimetic electrode material can be formed using electrospinning and other related processes. The biomimetic electrode may facilitate efficient charge transport from ionically conductive tissue to the electronically conductive electrode, and may induce surrounding tissue to attach or interface directly to the implanted device, increasing the biocompatibility of the device.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/237,121, filed on Sep. 24, 2008, now published as PublishedApplication No. 2009/0105796, entitled “Fibrous Electrode Material”,which claims the benefit of Provisional Application Ser. No. 60/981,221,filed Oct. 19, 2007, entitled “Fibrous Electrode Material”, which areboth incorporated herein by reference in their entireties for allpurposes.

TECHNICAL FIELD

This invention relates to body implantable medical devices, and moreparticularly, to implantable electrodes for sensing electrical impulsesin body tissue or for delivering electrical stimulation pulses to anorgan or a nerve.

BACKGROUND

Cardiac pacing leads are well known and widely employed for carryingpulse stimulation signals to the heart from a battery operated pacemakeror other pulse generating means, as well as for monitoring electricalactivity of the heart from a location outside of the body. Electricalenergy is applied to the heart via an electrode to return the heart tonormal rhythm. Some factors that affect electrode performance includepolarization at the electrode/tissue interface, electrode capacitance,sensing impedance, and voltage threshold. In all of these applications,it is highly desirable to optimize electrical performancecharacteristics at the electrode/tissue interface.

Surface and bulk materials currently used as electrodes for biomedicaldevices may result in inflammation in the vicinity of the implanteddevice and/or the formation of fibrous scar tissue. Such scar tissue maydiminish signal transduction between the tissue and the device. Onepotential characteristic of inflammation and/or scar tissue is adeficiency of fluid at the electrode-tissue interface.

SUMMARY

According to one embodiment, the present invention is a medicalelectrical lead. The medical electrical lead includes a lead body havinga conductor extending from a proximal end to a distal end. The proximalend of the lead body is adapted to be connected to a pulse generator. Atleast one electrode is operatively connected to the conductor. Accordingto one embodiment of the present invention, the electrode includes afibrous matrix including a conductive polymer and an ion conductingpolymeric material. The electrode may also include a pseudo-capacitivematerial dispersed within the fibrous matrix.

According to another embodiment, the present invention is a method offorming an electrode. The method includes providing a collectionsubstrate and a dispensing device. The dispensing device includes afirst dispensing portion and a second dispensing portion. A firstpolymeric material is introduced into the first dispensing portion. Asecond polymeric material is introduced into the second dispensingportion. Next, an electrode needle is positioned into contact with thefirst polymeric material. An electrical potential difference is appliedbetween the collection substrate and the electrode needle to causelocalized charge injection into the first polymeric material.Optionally, an electrical potential difference may also be appliedbetween the collection substrate and a second electrode needle (if used)to cause localized charge injection into the second polymeric material.The first and second polymeric materials are electro-staticallydischarged from the dispensing device toward the collection substrate.

According to yet another embodiment, the present invention is a methodof forming an electrode material. According to this embodiment, themethod includes electrospinning at least one polymeric material to forma plurality of fibers, collecting the electro-spun fibers on acollection substrate, and forming an electrode including a fibrousmatrix from the electro-spun fibers.

While multiple embodiments are disclosed, still other embodiments of thepresent invention will become apparent to those skilled in the art fromthe following detailed description, which shows and describesillustrative embodiments of the invention. Accordingly, the drawings anddetailed description are to be regarded as illustrative in nature andnot restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a lead and a pulse generator according toan embodiment of the present invention.

FIG. 2 is a partial cross-sectional view of the lead shown in FIG. 1according to an embodiment of the present invention.

FIGS. 3A and 3B are cross-sectional, schematic views of an electrodeaccording to various embodiments of the present invention.

FIG. 4 is an end, cross-sectional view of a conductive fiber used toform an electrode according to an embodiment of the present invention.

FIG. 5 is a cross-sectional view of a conductor including a conductivefiber.

FIG. 6 is a schematic view of an apparatus used to form a fibrous matrixaccording to an embodiment of the present invention.

FIG. 7 a schematic view of an apparatus used to form a fibrous matrixaccording to another embodiment of the present invention.

FIG. 8 is a close-up, schematic view of the dispensing device shown inFIG. 7 according to an embodiment of the present invention.

FIG. 9 is a flow chart of a method of making a fibrous matrix accordingan embodiment of the present invention.

While the invention is amenable to various modifications and alternativeforms, specific embodiments have been shown by way of example in thedrawings and are described in detail below. The intention, however, isnot to limit the invention to the particular embodiments described. Onthe contrary, the invention is intended to cover all modifications,equivalents, and alternatives falling within the scope of the inventionas defined by the appended claims.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings which form a part hereof, and in which is shown byway of illustration specific embodiments in which the invention may bepracticed. These embodiments are described in sufficient detail toenable those skilled in the art to practice the invention, and it is tobe understood that other embodiments may be utilized and that structuralchanges may be made without departing from the scope of the presentinvention. Therefore, the following detailed description is not to betaken in a limiting sense, and the scope of the present invention isdefined by the appended claims and their equivalents.

FIG. 1 is a schematic view of a medical electrical lead 10 coupled to apulse generator 14. The lead 10 includes one or more electrodes 50 todeliver pacing energy to a patient's heart and/or to sense and receiveelectrical signals from a patient's heart. Alternatively, the lead 10could be utilized for neuro-stimulation or other body implantableapplications.

The pulse generator 14, which can be implanted in a surgically-formedpocket in a patient's chest or other desired location, includes a powersupply such as a battery, a capacitor, and electronic components toperform signal analysis, processing, and control. For example, the pulsegenerator 14 can include microprocessors to provide processing andevaluation to determine and deliver electrical shocks and pulses ofdifferent energy levels and timing for ventricular defibrillation,cardioversion, and pacing to a heart in response to cardiac arrhythmiaincluding fibrillation, tachycardia, and bradycardia.

FIG. 2 is a partial, cross-sectional view of the lead 10 shown inFIG. 1. As shown in FIG. 2, the lead 10 includes an elongated, flexiblelead body 20 having a proximal portion 24 and a distal portion 28. Inone embodiment of the present invention, the lead body 20 includes alumen for receiving a guiding element such as a guidewire or a stylet.The lead body 20 also includes one or more conductors 30 extending froma proximal end 32 to a distal end 36 of the lead body 20. The proximalend 32 is configured to be operatively connected to the pulse generator14 via a connector 40.

The conductor 30 can include one or more conductive wires or fibers,which are operatively connected to one or more electrodes 50 located onthe lead body 20. A plurality of discrete conductors may be utilizeddepending on the number of electrodes 50 employed.

FIGS. 3A and 3B are cross-sectional, schematic views of the electrode 50according to various embodiments of the present invention. According toone embodiment of the present invention, as shown in FIG. 3A, theelectrode 50 includes a fibrous matrix of polymeric material including aconductive polymer and an ion conducting polymeric material. Accordingto another embodiment of the present invention, as shown in FIG. 3B, theelectrode 50 includes a conductive base 55 and a coating 60. The base 55can be formed from platinum, stainless steel, MP35N, a platinum-iridiumalloy or another similar conductive material. The coating 60, which isdisposed on at least a portion of the conductive base 55, includes afibrous matrix formed from a conductive polymer and an ion conductingpolymeric material. According to one embodiment of the presentinvention, the coating is disposed over substantially all of theconductive base 55.

Conductive polymers, as used herein, include intrinsically conductivepolymers and conductor-filled polymers. Examples of conductive filledpolymers include polyurethanes, silicone elastomers, or other polymericmaterials that are compounded with a conductive material such as carbonnanoparticles. Intrinsically conductive polymers are conductive withoutrequiring a non-polymeric conductive filler or coating, such as ametallic compound or carbon. Intrinsically conductive polymers includealternating single and double bonds forming a conjugated backbone thatdisplays electronic properties. Charge in intrinsically conductivepolymers is transported along and between polymer molecules via chargecarriers generated along the conjugated backbone.

Intrinsically conductive polymers may include dopants to enhance theirconductivity. Dopants may also help to control the conductivitycharacteristics of the polymer. The conductivity of intrinsicallyconductive polymers can generally range from semi-conducting to superconducting, depending upon the doping levels. Some intrinsicallyconductive polymers may also exhibit a quasi-redox behavior that ishighly reversible giving them pseudo-capacitive properties. Examples ofintrinsically conductive polymers include, but are not limited to, thefollowing: polypyrrole, polyacetylene, polythiophene,polyethylenedioxythiophene, poly (p-phenyl vinylene), polyaniline,polynapthalene, other suitable conductive polymers, and mixturesthereof.

According to one embodiment of the present invention, the conductivepolymer is an intrinsically conductive polymer. According to anotherembodiment of the present invention, the conductive polymer is aconductive-filled polymer.

The inclusion of a conductive polymer into the fibrous matrix mayincrease its biocompatibility, reduce pacing thresholds, and improvesensing performance. Additionally, the inclusion of a conductive polymermay present an organic interface to biological tissue instead of ametallic interface (e.g. metallic electrode), which may facilitate afavorable biological response to the implant. The inflammatory andhealing response of the tissue at the local site may be controlledand/or altered to reduce necrosis in the area next the to the lead andto reduce the thickness of any resultant fibrotic capsule.

As used herein, the term ion conducting polymeric material means anypolymeric material capable of conducting ions and includes polymerelectrolytes, polyelectrolytes, ionomers, and composites andcombinations thereof.

In one embodiment, the ion conducting polymeric material is a polymerelectrolyte. Polymer electrolytes can combine the desirable mechanicalproperties of polymers (e.g., ease of fabrication, low density,flexibility, etc.) with good conductivity. Polymer electrolytes areionically conducting, solvent-free materials generally composed ofalkali salts dissolved in a polymer matrix. According to one embodiment,a polymer electrolyte may include a lithium salt dissolved within apoly(ethylene oxide) (PEO) matrix. The ionic conductivity of the polymerelectrolyte material is due to the mobility of cations and theircounterions when subjected to an electric field within the polymerelectrolyte material. According to other embodiments, useful polymerelectrolytes can also include block co-polymers of polyethylene oxidewith polyamide, polyimide, or polyurethane. Other examples include, butare not limited to, the following: polysiloxane, polymethyl methacrylate(PMMA), polyvinyl acetate (PVA), polyvinylpyrrolidone (PVP), andpolylactic acid (PLA).

According to a further embodiment of the present invention, the polymerelectrolyte is a hydrophilic polymer electrolyte. The presence of ahydrophilic polymer electrolyte within the fibrous matrix may correctany anomalous ion diffusion at the electrode/tissue interface resultingfrom a reduction of fluid as a consequence of inflammatory tissueresponses at the local site, resulting in an increase in impedance and adistortion in the charge transfer characteristics.

According to another embodiment of the present invention, the ionconducting polymeric material is a polyelectrolyte. Polyelectrolytes,including ion exchange polymers, may be useful in forming the fibrousmatrices according to the various embodiments of the present invention.Polyelectrolytes are polymers whose repeating units bear an electrolytegroup. These groups will dissociate in aqueous solutions, making thepolymers charged. Polyelectrolytes can be positively (cationic) ornegatively (anionic) charged. Some polymer electrolytes include bothcationic and anionic repeating groups. Exemplary polyelectrolytesinclude: polystyrene sulfonate (PSS), polyglutamic acid, Nafion®, andmixtures thereof.

The presence of an ion conducting polymeric material along with aconductive polymer within the fibrous matrix forms a matrix that is botha good ion and electron conductor. Additionally, the incorporation of anion conducting polymeric material in the fibrous matrix may allow thefibrous matrix to be permeable to small molecules, resulting in aneffective electrode surface area and the elimination of the abruptelectrode-tissue interface. The high electrode surface area combinedwith the elimination of the abrupt electrode-tissue interface may allowfor a more efficient charge transfer process and may allow electriccoupling to the surround neural or vascular tissue.

According to yet a further embodiment of the present invention, thefibrous matrix may include a plurality of conductive fibers doped with ahydrophilic polymer electrolyte.

According to another exemplary embodiment of the present invention, thefibrous matrix can also include a pseudo-capacitive material. Apseudo-capacitive material is a material that is capable of undergoing areversible faradaic process, such as an oxidation/reduction (redox)reaction. Pseudo-capacitors are capable of storing large amounts ofcharge, and can serve as high or ultra-high capacitors. When thecapacitance of a material is measured using cyclic voltammetry,capacitance is directly proportional to the measured current. Someconductive polymers such as polyaniline and polythiophenes can alsobehave as pseudo-capacitors. Exemplary pseudo-capacitive materialsinclude, but are not limited to, transition metal oxides such as iridiumoxide, ruthenium oxide, rhodium oxide, osmium oxide, titanium oxide,tantalum oxide, zirconium oxide, and combinations thereof. Othermaterials capable of enhancing the capacitive properties of the fibrousmatrix include carbon, metal-carbon composites, nitrides, oxy-nitrides,or other materials with similar high capacitance characteristics. Theincorporation of one or more of these materials into the fibrous matrixmay further enhance the capacitance properties of the pseudo-capacitivematerials.

The pseudo-capacitive material may be dispersed throughout the fibrousmatrix in the form of microparticles or nanoparticles. In someembodiments, the dispersion of pseudo-capacitive particles can be auniform dispersion of particles.

The amount of pseudo-capacitive material present in the fibrous matrixmay be helpful for maintaining the electrode potential within a safeelectrochemical window for pacing. The amount of pseudo-capacitivematerial present in the fibrous matrix should be sufficient to maintainthe electrode potential within a safe electrochemical window for pacing.A safe electrochemical window for pacing can be defined as the potentialrange within which only reversible reactions occur. This can also bereferred to as the charge injection limit. In general, the potentiallimits of the electrochemical window for pacing are the hydrolysis ofwater to oxygen and protons (anodic limit) and of hydrogen to hydroxideions (cathodic limit) which is approximately 2V. Within this potentialrange a number of additional reactions may also occur.

reduction E°/volts 1 O2 + 4H+ + 4e− ® 2H2O +1.229 2 Ag+ + e− ® Ag+0.7996 3 Cu2+ + 2e− ® Cu +0.3419 4 Fe2+ + 2e− ® Fe −0.447 5 Zn2+ +2e− ® Zn −0.7628 6 2H2O + 2e− ® H2 + 2OH— −0.83

The voltage drop values at the electrode tissue interface remain withinthe cathodic and anodic potential limits of the hydrolysis of waterresulting in a high capacitance of the electrode.

According to an embodiment of the present invention, the amount ofpseudo-capacitive material present in the fibrous matrix should besufficient to maintain the electrode potential within an electrochemicalwindow of about 2 V. According to a further embodiment of the presentinvention, the fibrous matrix includes a pseudo-capacitive materialpresent in an amount no greater than about 35 wt % of the total weightof the fibrous matrix.

According to an exemplary embodiment of the present invention, thefibrous matrix includes a plurality of fibers, each fiber including acore and a shell. FIG. 4 is a cross-sectional view of a fiber 70including a core 72 and a shell 74. The core 72 includes a conductivepolymer and the shell 74 includes a polymer electrolyte.

According to another embodiment of the present invention, the fibrousmatrix can include a plurality of conductive polymer fibers inter-mixedwith a plurality of polymer electrolyte fibers. According to yet anotherembodiment of the present invention, the fibrous matrix may include acore having a plurality of conductive polymer fibers surrounded by ashell including a plurality of polymer electrolyte fibers.

According to a further embodiment of the present invention, thepseudo-capacitive material can be dispersed within the conductivepolymer fibers. According to yet another embodiment of the presentinvention, the pseudo-capacitive material may be dispersed within theion conducting polymeric fibers.

According to other embodiments of the present invention, the conductor30 extending from the proximal end 32 to the distal end 36 of the leadbody 20 can also be formed from one or more conductive polymer fibers.FIG. 5 is a cross-sectional view of conductor 30 comprising a conductivefiber 80. According to one embodiment of the present invention, as shownin FIG. 5, the conductive fiber 80 includes a core 85 including aconductive polymer and a shell 90 including an insulative polymer.According to various exemplary embodiments, the conductive fiber 80 caninclude a single conductive fiber strand or a plurality of conductivefiber strands wound together to form a single conductive fiber.

A conductor 30 formed in this manner could extend from the proximal end32 of the lead 10 to one or more electrodes 50. At each electrode 50,the conductive polymer fibers 80 could be combined with the polymerelectrolyte fibers to form the fibrous matrix and the electrode site. Inembodiments in which multiple electrodes 50 are used, multiple discreteconductors formed from the conductive polymer fibers could be utilized.

According to one embodiment of the present invention, an electrospinningtechnique may be used to form the fibrous matrix and/or conductoraccording to the various embodiments of the present invention asdescribed above. Electrospinning of liquids and/or solutions capable offorming fibers, are shown and described, for example, in U.S. Pat. No.4,043,331 which is incorporated herein by reference. FIG. 6 is aschematic view of a typical apparatus 100 used for electrospinning. Theapparatus 100 includes a dispensing device 104, for example a syringe,having a metallic needle 108, a syringe pump (not shown), a high-voltagepower supply 112, and a grounded collection substrate 116. A solution120 containing one or more polymeric materials is loaded into thesyringe and is then delivered to the needle tip 124 by the syringe pump,forming a suspended droplet at the needle tip 124.

At a characteristic voltage, the droplet forms a Taylor cone and a finejet of polymeric material releases from the surface in response to thetensile forces generated by interaction of an applied electric fieldwith the electrical charge carried by the jet. This jet can be directedto the grounded collector and collected as a continuous web of fibers.

Fibers ranging from about 50 nm to about 5 μm in diameter can beelectrospun into a non-woven nanofiber mesh. Due to the small fiberdiameters, electrospun fiber matrices inherently possess a very highsurface area and a small pore size.

Electrospinning may also be used to produce fibers having a core-shellconfiguration, as described in Advanced Materials 2004, 16, No. 17, Sept3, which is incorporated herein by reference in its entirety. To producea fiber having a core-shell configuration, a spinneret that allows forthe coaxial extrusion of two fluids is used. The spinneret includesconcentric inner and outer tubes by which two fluids are introduced intothe spinneret. The spinneret keeps the fluids separate as they arecharged and emitted from the nozzle. At least one fluid, usually thefluid forming the shell, is an electrospinnable fluid.

According to another embodiment of the present invention, flow-limited,field-injection electrostatic spraying (FFESS) may be used to form thefibrous matrix. A FFESS apparatus and method is shown and described inUS Published Application No. 2007/0048452, which is incorporated hereinby reference in its entirety. FFESS allows electrically insulativematerials, or materials having a low dielectric constant to be used toform fibrous materials because the localized field emission or fieldionization can provide sufficient charge carries necessary forsuccessful electrospinning. Additionally, FFESS may facilitate moreprecise deposition and controlled growth of polymeric nanofibers andother nanostructures. Pseudo-capacitive nanoparticles can be dispersedwithin the polymeric solution from which the fibers composing thefibrous matrix are formed. FFESS may also facilitate the fabrication oflead bodies having very small outer diameters.

FIG. 7 is a schematic view of an apparatus 150 that is suitable for usein FFESS processes. Unlike in conventional electrospinning techniques, ahigh-intensity electric field is applied at the tip of a needle 154inserted within the tip 158 of the dispensing device 162 thus injectingcharge into the surrounding solution 166. The resultant fibers arecollected on a substrate 170 serving as a counter electrode.

FFESS also may be used to produce fibers having a core-shellconfiguration. FIG. 8 is a close-up schematic view of the dispensingdevice 162 shown in FIG. 7 used to produce fibers having a core-shellconfiguration according to an embodiment of the present invention. Asshown in FIG. 8, the dispensing device 162 can include a firstdispensing portion 180 and a second dispensing portion 184. The firstdispensing portion 180 may be positioned within the second dispensingportion 184. The needle 154 is inserted into the polymeric materialrequiring the charge injection. Two needles may be used if the polymericmaterials in both the first and second dispensing portions 180, 184require charge injection in order to form an electro-spun fiber. Thisconfiguration allows for fibers having a core including a firstpolymeric material surrounded by a second polymer material. For example,the dispensing device 162 as shown in FIG. 8 may be useful in forming afiber or a fibrous matrix having a core including a conductive polymerand a shell including a polymer electrolyte or another ion conductingpolymeric material, according to the various embodiments of the presentinvention, as described above.

FIG. 9 is a flow chart 200 of a method of forming a fibrous matrix usingFFESS according to an embodiment of the present invention. First, acollection substrate is provided to collect the fibers formed during theelectrospinning process (block 204). A dispensing device from which thepolymeric solution is discharged is also provided (block 208). Accordingto one embodiment of the present invention, the dispensing deviceincludes a first dispensing portion and a second dispensing portion. Afirst polymeric material is introduced into the first dispensing portionof the dispensing device, typically via a pump or other suitabledelivery device (block 212). Similarly, a second polymeric material isintroduced into the second dispensing portion of the dispensing device(block 216). An electrode needle, such as a sharpened tungsten needle,is positioned within the first dispensing portion such that it is incontact within the first polymeric material (block 220). Depending onthe physical properties of the second polymeric material, a secondelectrode needle may also be placed into contact with the secondpolymeric material (block 224). Finally, localized charge injection isinduced into the first and/or second polymeric materials by applying anelectrical potential difference between the collection substrate and theelectrode needle(s) (block 228). The first and second polymericmaterials are electro-statically discharged from the dispensing deviceand collected on the collection substrate in the form of fibers or afibrous matrix (blocks 232 and 236). According to a further embodimentof the present invention, pseudo-capacitive particles may be dispersedin the first and/or second polymeric materials.

The electrode material, electrodes, and coatings contemplated byembodiments of the present invention include electrode materials,electrodes, and electrode coatings which have low biodegradability, lowelectrical impedance, long-term electrical stability under in vivoconditions, are mechanically soft (e.g. flexible), and are biomimetic.The large surface area can facilitate charge transfer between theelectrode and target tissue. Additionally, the pliability andflexibility of the electrode and electrode coatings may facilitatedecreased mechanical strain at the interface between the soft tissue andthe hard device surface compared to a conventional electrode.

The electrode materials, electrodes, and electrode coatings of thepresent invention may provide electrodes and electrode coatings that areelectrically stable over time following implantation in tissue.Additionally, the electrode materials, electrodes, and electrodecoatings may be relatively non-biodegradable yet biocompatible,eliciting lower levels of immuno-reactivity than commonly usedconductive substrate materials. According to various embodiments of thepresent invention, the electrodes or electrode coatings may be readilymodified to contain a variety of bioactive agents. For example, proteinscan be incorporated into the conducting polymer material via a varietyof methods such as electrochemical deposition, covalent linkage, andentrapment in the polymer matrix.

The electrode materials, electrodes, and electrode coatings may be usedin a wide variety of applications including, but not limited to, thefollowing: cardiac pacing and sensing, neuro-stimulation, cochlearstimulation, wound closure, pacing seeds, heart tissue constructs, andother applications in which improvement of the electrochemicalinteractions at the electrode-tissue interface may be desirable.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the described features. Accordingly, thescope of the present invention is intended to embrace all suchalternatives, modifications, and variations as fall within the scope ofthe claims, together with all equivalents thereof.

1. A medical electrical lead comprising: an elongated lead body having aproximal end adapted to be coupled to a pulse generator and a distalend; at least one conductor extending within the lead body from theproximal end in a direction toward the distal end of the lead body; andat least one electrode located on the lead body operatively coupled tothe at least one conductor, the electrode comprising a fibrous matrixincluding a plurality of fibers having a core comprising a firstpolymeric material surrounded by a shell comprising a second polymericmaterial.
 2. The medical electrical lead according to claim 1, whereinthe electrode further comprises a conductive base material and thefibrous matrix is disposed over and in contact with at least a portionof the conductive base material.
 3. The medical electrical leadaccording to claim 1, wherein the first polymeric material comprises aconductive polymer.
 4. The medical electrical lead according to claim 1,wherein the second polymeric material is an ion conducting polymericmaterial.
 5. The medical electrical lead according to claim 1, whereinthe first polymeric material comprises a conductive polymer selectedfrom the group consisting of polypyrrole, polyacetylene, polythiophene,polyethylenedioxythiophene, poly (p-phenyl vinylene), polyaniline,polynapthalene, and mixtures thereof.
 6. The medical electrical leadaccording to claim 1, wherein the second polymeric material is selectedfrom the group consisting of polystyrene sulfonate, polyglutamic acid,NAFION®, and mixtures thereof.
 7. The medical electrical lead accordingto claim 1, wherein the electrode further comprises a pseudo-capacitivematerial dispersed within the fibrous matrix.
 8. The medical electricallead according to claim 1, wherein the fibrous matrix further includes abioactive agent.
 9. A body implantable device comprising: a conductor;and an electrode operatively coupled to the conductor, the electrodecomprising a fibrous matrix including a plurality of fibers having acore comprising a first polymeric material surrounded by a shellcomprising a second polymeric material.
 10. The body implantable deviceaccording to claim 9, wherein the electrode further comprises aconductive base material and the fibrous matrix is disposed over and incontact with at least a portion of the conductive base material.
 11. Thebody implantable device according to claim 9, wherein the firstpolymeric material comprises a conductive polymer.
 12. The bodyimplantable device according to claim 9, wherein the second polymericmaterial is an ion conducting polymeric material.
 13. The bodyimplantable device according to claim 9, wherein the first polymericmaterial comprises a conductive polymer selected from the groupconsisting of polypyrrole, polyacetylene, polythiophene,polyethylenedioxythiophene, poly (p-phenyl vinylene), polyaniline,polynapthalene, and mixtures thereof.
 14. The body implantable deviceaccording to claim 9, wherein the second polymeric material is selectedfrom the group consisting of polysiloxane, polymethyl methacrylate,polyvinyl acetate, polyvinylpyrrolidone, and polylactic acid.
 15. Thebody implantable device according to claim 9, wherein the electrodefurther comprises a pseudo-capacitive material dispersed within thefibrous matrix.
 16. The body implantable device according to claim 9,wherein the fibrous matrix further includes a bioactive agent.
 17. Amedical electrical lead comprising: a lead body having a proximal endadapted to be coupled to a pulse generator and a distal end; and aconductor extending from the proximal end in a direction toward thedistal end of the lead body, the conductor comprising at least one fiberhaving a core comprising a first polymeric material surrounded by ashell comprising a second polymeric material.
 18. The medical electricallead according to claim 17, wherein the first polymeric material is aconductive polymer and the second polymeric material is an insulativepolymer.
 19. The medical electrical lead according to claim 17, whereinthe conductor comprises a plurality of fibers, each fiber having a corecomprising the first polymeric material surrounded by a shell comprisingthe second polymeric material.
 20. The medical electrical lead accordingto claim 17, further comprising an electrode operatively coupled to theconductor, the electrode comprising a fibrous matrix including aconductive polymer.
 21. A method of forming a fibrous electrode materialcomprising: electrospinning a first polymeric material and a secondpolymeric material to form a fibrous matrix comprising a plurality ofelectrospun fibers, each fiber having a core comprising the firstpolymeric material surrounded by a shell comprising the second polymericmaterial; and forming an electrode comprising the electrospun fibrousmatrix.
 22. The method according to claim 21, further comprisingcollecting the electrospun fibers on a surface of an electrode.
 23. Themethod according to claim 21, further comprising coupling the electrodeto a conductor.